Based on the CFD-DEM method,numerical simulations in gap-graded sandy gravels with different fines contents(mass fraction,similarly hereinafter)and gap ratios(GR)were carried out to investigate the combined effects of fines content and gap ratio on suffusion from macro and micro perspectives.The results show that the erosion rate increases with increasing GR.No particle migration occurs within the soil samples when the GR is smaller than 3,demonstrating good internal stability.Furthermore,GR has a notable effect on suffusion behavior when the fines content(FC)varies.For instance,with a relatively low FC(e.g.,FC is 15%),fine particles play a limited role in stress transfer.During the erosion process,the sample volume,the strong contact force chain network,and the stress reduction coefficient remain relatively unchanged.This indicates that the increase in erosion rate is primarily attributed to the increased pore diameter among coarse particles and the loss of weak-contact fines.On the contrary,when the FC is relatively high(e.g.,FC is 35%),the fine particles actively participate in stress transfer,and an increase in GR can result in a reduction in the number of coarse particles.The loss of fine particles easily leads to the collapse of the entire force chain system,causing the skeleton particles to deform and rearrange,releasing more constrained particles and intensifying the loss of fine particles.Therefore,the main reason for the increasing erosion rate is the combined effect of the increasing pore diameter among coarse particles and the continuous deformation of the soil skeleton during suffusion.
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